Open Spirometry

A spirometer is a medical device used to measure pulmonary function. In its most basic form, it measures air flow, and either directly or via integration, air volume. Most commercial units rely on some form of a mechanical turbine as a sensor, but there are a number of ways one might measure said flow velocities.

Spirometers are pretty high priced units $1000 plus… Considering I can buy a microprocessor based wind measurement device (which is not unlike a spirometer) for under $15 including shipping, there is a lot of money on the table. Granted, a spiro is more sensitive… but rather than the delrin bearings in a wind device, a couple jewel bearings do not equate to a 20X multiplier in msrp. The worst part is that high prices preclude the use of sprios and other medical devices in world markets where $1000 is just too expensive. At some point, it will be solved once an outfit decides to canibalize the world market for spirometers… but that could take some time if it ever happens. One can look to China, and they have a spirometer for under $300, but such is a far cry from the $30-50 range.

I’m guess part of the problem is Chinese and other medical device manufacturers are likely to be thwarted left and right by govt regulators to say nothing of intellectual property law gamesmanship. Alas, sooner or later it is likely to happen as markets will force the issue, but it is a matter of when. As a buddy who grew up in China used to tell me the mantra of manufacturing plants he knew about… if junk makes money, we will make it. If quality makes money, we will make it… if we can’t make a quick buck with ease, we wont touch it. Ultimately it comes down to when someone can make decent money with sub $50 units.

Some folks over at UW-Madison started openspirometry some years back to address the insane price of commercial devices leading to a lack of diagnostics in less economically advantage cultures. It looked to be a great student project… alas, it sort of died on the vine after a few years, so I checked into it.



Hmmm… I did a little poking around to see where things are in the commerical world. I found this patent on injection molding turbines to make disposable units pretty fascinating. A little more digging and wowzers, 200 disposable turbine and mouth piece assemblies for just a tad under $300. Or in plain and simple terms, labor and materials to make these mouth piece turbine assemblies is likely in the $0.25 – $0.50 range. If such were to be paired with wind instrument electronics (photo tach, micro processor, and LCD) the problem is really close to being technically solved. Alas, its unlikely that MIR will be really pleased with someone buying hundreds of thousands of turbines w/o their $1000 support electronics. Likewise until the patent runs out, injection molding a 1 piece mouth piece turbine assembly is pretty hard to work around from an intellectual property point of view.

It would be easy to open source the phototach and user interface… but the problem remains with the basic sensor. I’l have to think on this.

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1 Comment

  1. Ron –

    The devil is in the details. It is easy using any number of different flow sensors to make a spirometer that is sort-of accurate, but much more difficult to make one that is clinically useful. Take a look at the ATS-ERS guidelines:( and you will see they are looking for a minimum of +/- 3% accuracy. Expiratory airflow is much more difficult to measure than you would expect and has problems that measuring wind airflow does not have. Specifically: inhalation and exhalation airflow differs in humidity, temperature, gas concentration and viscosity. Most of the inexpensive “personal” spirometers you see on Ebay and Amazon do not meet ATS-ERS standards. Inaccurate results will give you too many false positives and false negatives, and what use is that? This is not to say that an open spirometer could not be created and it is something I would like to see happen, just that creating an open spirometer that is clinically useful is going to take some work and attention to detail.

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